Acoustic cameras are devices which collect sound signals from the environment with a microphone array, and which characterize the collected sound signals in some desired way. The acoustic camera may comprise an optical camera as well. Because the distances between each microphone and a specific sound source usually vary, the time delay differences between the received audio signals in each of the microphones can be taken into the analysis. Because the direction of the incoming sound and the time delays are related to one another, a calculation unit of the acoustic camera is able to achieve direction and power information of the acoustic signal. Furthermore, the array of microphones may be tuned in some way in order to create a specifically directed beam in a desired direction for the microphone array.
US 2014/0241548 (“Kim”) discloses an acoustic camera with a MEMS microphone array and the internal structure of the microphone array. The structure is a branched one where there can be 2-10 microphones per branch and 2-10 radial-type of branches. A single branch can be formed in a straight-line shape or in a spiral form. Kim shows an acoustic visualization by colors in the display.
US 2014/0192201 (“Benoit”) discloses a passive acoustic signal measurement device. The main issue in Benoit is to move the microphone array (or an acoustic antenna) physically across different places of a space while the main device stays in a fixed position. The microphone array is thus connected to the device through cablings. Benoit discloses a round-shaped support structure where the microphones can be attached, also in a round-shaped planar arrangement. Also two optical distance sensors are attached to the support. The data processing electronics are included in the support structure as well. The number of microphones in Benoit is 3-16, and preferably there are 8 microphones. Data can be sent wirelessly to an external processing unit. Benoit can have a handle for handheld use, or the device can be fixed to a tripod. The display of Benoit may also have a touch screen functionality. The acoustic area where Benoit is capable to sense acoustic signals, is from 20 Hz . . . 20 kHz. From the measured acoustic signal levels in the area under investigation Benoit creates a plurality of values in a grid-form. A photograph may be taken, and on top of the taken optical image, the device can add a colored image or a grey-scale image representing created grid of numeral values. The thickness or depth dimension of the device of Benoit can be even less than 5 cm. No MEMS microphones are discussed in Benoit.
The problem of the above solutions is that many of the prior art solutions are physically quite large, and thus they require unnecessarily large space for the housing of the acoustic camera. This further leads in more difficult handling of the acoustic camera, decreasing its usability in various spaces and different measurement situations. Also the frequency range is very limited in some known solutions (20 Hz-20 kHz), and the resolution and accuracy of the acoustic picture is limited if there are only eight microphones in use. Furthermore, prior art publications do not perform any classification or naming for the measured acoustic emissions.